Ask the Engineer: Micro-Molding – Prototyping Challenges

Here again is another potential barrier you may face when developing parts for micro-molding. Prototyping as you know is a regular part of any design process. There are also many different reasons one might need to prototype a part. Certainly mechanical functionality is a key driver, but cosmetics, material compatibility or longevity may also play a huge factor in how you approach the prototyping phase.

If you have ever sent out a micro part for quote to a prototyping service bureau then, like some of the material selection responses we saw, you have probably run into a few challenges yourself. Prototyping for micro parts or features can be a major hurdle even to the point of changing your part design, if you can’t achieve what you need to move your project forward. However, unlike material selection, prototyping is not just a “try it” kind of process in a lot of ways and there are definitely limiting factors in today’s commercially available prototyping processes.

What can you do?

In order to answer that question, we built another test part (Fig.1). This time, we built a part with the size and type of features we see on a regular basis. The goal was to send this part out to be prototyped by as many of the common readily-available prototyping processes we could find.

Now this study was not to judge these different processes themselves. They all have places where they are very effective. IN some cases, any of the processes could produce what you may need in a prototype. However, we wanted to look at the more extreme side of the equation.

We tried to approach this as any of you would. We designed a part and searched to have it prototyped. We sent the part out for quote to server bureaus that offered these 11 different processes:

Stereolithography (SLA)

3D Printing

PolyJet

Fusion Deposit Modeling (FDM)

Selective Laser Sintering (SLS)

Laminated Object Manufacturing (LOM)

Cast Urethanes

Machining/ Rapid Tooling

Rapid Injection Molding (RIM)

Standard Hard Tooling

Of the 11 different processes, five responded and the rest “no quoted” the opportunity. SLA, PolyJet, Machined and Standard Hard Tooling all netted fairly good results. The fifth one we received was from a 3DS printer. It appeared more like a sugar cube, and only the basic square shape was produced.

Originally when we embarked on this study, we thought we might have to get the scope out and measure the fine details in order to determine which parts met print. However, as you can see, the feature performance is fairly obvious.

Before you call one process successful or not, you will have to judge it against your needs. For example, Fig. 3 is the top side of the part. The row at the top is a series of 250μm diameter lenses. The “whiter” the image, the more “polished” the finish is. You can see here the molded part was the only one to replicate the highly polished surface (which is should). The point being, if that’s what you need for your prototype to function, your options may be very limited. This can also be the case for other needs like feature definition or tolerance requirements.

In this Fig.4, you can really see the different outcomes. The thin tabs final shapes are quite different. Again, your part will dictate what’s important in a prototype and can determine how you may approach the process.

It’s also important to note that another barrier with this stage of development is cost and speed. If hard tooling is what you determine as the only process to make your prototype function as needed, the cost and speed can be a limiting factor. If you are expecting hard tooling to be finished parts in 1 day for $1000, more like some of the rapid services out there, you may hit a barrier.

While new advancements in rapid prototyping are being achieving all the time, since they are working to push the limits in their own way, there isn’t really a rapid micro molding process. There are quick mold programs out there, but one usually talks about a week or two, not hours.

The point is to know that prototyping for micro parts can be challenging not only in producing the parts but in the time and cost you may be used to. Factor that in as you design for micro molding.

Next week, we will discuss looking beyond the part at Metrology, Handling and Packaging; and Size and Features. Stay tuned!

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